The present invention relates to a communication system corresponding to an OSI (Open Systems Interconnection) reference model composed of layers 1 to 7, and to a control signal processing apparatus for sending and receiving a frame containing control information through the layer 1 link (physical signal link) and the layer 2 link (logical link), and a communication system including the same control signal processing apparatus.
In a next-generation mobile radio communication network, it is expected that a network performs an authentication process on a user (caller) at the time of calling. In the authentication process, authentication information is exchanged between a mobile station and a network when connecting the mobile station to the network, but the authentication information results in being fairly great in quantity in order to prevent an illegal utilization. In order to shorten a connection delay, it must not take a long time to exchange the authentication information. In a next-generation mobile radio communication network, therefore, it is necessary to heighten the ability (physical data transfer rate) of the layer 1 link (physical signal link) used in calling and to exchange the authentication information in a short time between a mobile station and the network.
After a connecting process has been finished and a mobile station comes into a communicatable state, however, the quantity of control information to be exchanged between the mobile station and the network side is a little, and therefore a required ability of the physical signal link becomes remarkably lower in comparison with that at the time of originating a call.
Accordingly, at the present time, a communication method is being examined which allocates a temporary physical signal link to a user at the time of originating a call and then allocates newly a physical signal link lower in ability instead of the temporary physical signal link after validity of the call has been confirmed by an authentication process.
Furthermore, a communication method is being examined which can not only perform such a control at the time of originating a call but also perform switching over of a physical signal link without delay in response to a requirement from signal processing performed by an upper layer process and effectively utilize a limited channel resource.
Meanwhile, when performing such xe2x80x9cswitching over of a physical signal linkxe2x80x9d using with a conventional method for switching over a physical signal link in a mobile radio communication network, it is necessary to release once an established layer 2 link (logical link) and then newly re-establish the layer 2 link.
If a physical signal link switching-over method accompanied by such switching over of the layer 2 link is applied to a next-generation mobile radio communication network, however, it is necessary to release and re-establish the layer 2 link each time a physical signal link is re-established, and so a problem happens that an overhead operation is increased.
Furthermore, if the layer 2 link is re-established when a physical signal link is re-established, the information (frame) lost at the time of releasing the layer 2 link is not retransmitted in a new layer 2 link. Therefore, it is a possibility that an upper layer 3 signal (message) disappears and the control procedure reaches a deadlock.
The present invention has been provided in consideration of the above-mentioned circumstances, and a first object of it is to provide a control signal processing apparatus and a communication system capable of switching over a physical signal link for sending and receiving a control signal with a little overhead operation.
A second object of the invention is to reduce to the utmost a frame loss at the time of re-establishing a physical signal link.
In order to solve the above-mentioned problems, the present invention provides a control signal processing apparatus which has a control function for managing establishment and maintenance of a physical signal link and a logical link, and sends and receives frames including control signals through a physical signal link and a logical link which have been established, said control signal processing apparatus comprising;
a physical signal link switching-over means for switching over a physical signal link to be used in sending and receiving a control signal to a new physical signal link without releasing a logical link in response to a physical signal link switching-over request requiring to switch over a physical signal link to another physical signal.
According to this invention, since a physical signal link is switched over without releasing a logical link, it is possible to reduce an overhead operation for switching the physical signal link.
Examples of switching over a physical signal link are as follows:
a. A physical signal link switching over request is generated when a call is originated and an information channel has been established. A physical signal link for sending and receiving a control signal is then switched over to another physical signal link having a less capacity.
b. A physical signal link switching-over request is generated when performing a switching over of a bearer. A physical signal link for sending and receiving a control signal is then switched over to a physical signal link corresponding to a new bearer obtained after switching over.
c. A physical signal link switching-over request is generated when a plurality of calls are in communication and a call using a physical signal link for sending and receiving a control signal is finished. A physical signal link for sending and receiving a control signal is then switched over to a physical signal link corresponding to one of the remaining calls.
In a preferred embodiment of the invention, when a physical signal link switching-over request is given, the physical signal link switching-over means performs:
requesting establishment of a target physical signal link without releasing the logical link and starting to receive control signals using both of the target physical signal link and the original physical signal link;
switching over a physical signal link to be used for sending a control signal to the target physical signal link and requesting release of the original physical signal link after confirming that the target physical signal link has been established; and
switching over a physical signal link for receiving a control signal to only the target physical signal link after confirming that the original physical signal link has been released.
In this embodiment of the invention, since control signals are sent and received using both of a target physical signal link and an original physical signal link until the original physical link is released after the target physical signal link has been established, it is possible to avoid to the utmost a frame loss which may be caused by the switching over of a physical signal link.
In another preferred embodiment of the invention, a control signal processing apparatus further comprises:
a database for storing maximum frame length of each of available physical signal links;
selecting means for selecting a target physical signal link when said physical signal link switching-over request is given; and
a transmitting means for obtaining the maximum length corresponding to said target physical signal link from said database and for transmitting one or more frames having the maximum frame length and including the control signal.
In this embodiment of the invention, since it is possible to send a frame having the maximum length adapted to a physical signal link throughout before and after switching over the physical signal link, a high transmission efficiency can be kept even in case of switching over a physical signal link.
A control signal processing apparatus according to another embodiment of the invention is provided considering a case in which a frame transmitted from an opposite apparatus, which is provided on a mobile station of a mobile radio communication system, is lost, and the control signal apparatus request the switching over of a physical signal link before receiving a retransmission frame corresponding to the lost frame.
In such a case, a control signal processing apparatus according to the embodiment of the invention keeps a state where both of a frame corresponding to an original physical signal link and a frame corresponding to a target physical signal link can be received until the retransmission frame has been received.
According to this embodiment of the invention, it is possible to avoid to the utmost a frame loss which may be caused by switching over a physical signal link.
Furthermore, the invention provides a communication system comprising in a network a control signal processing apparatus which has a control function of managing establishment and maintenance of a physical signal link and a logical link, and sends and receives a frame containing a control signal through a physical link and a logical link which have been established, wherein;
said control signal processing apparatus is provided with a physical signal link switching-over means which switches over a physical signal link to be used in sending and receiving a control signal to a new physical signal link without releasing a logical link in response to a physical signal link switching-over request requiring to switch over a physical signal link to another physical signal link.
According to this invention, it is possible to switch over a physical signal link for exchanging a control signal between nodes in a network with a little overhead operation, and to effectively utilize resources.